DHCP Lease Grace Period Is Four Hours

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This article was previously published under Q261964

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SUMMARY

After a Dynamic Host Configuration Protocol (DHCP) client lease expires, it is not immediately scavenged from the database. A grace period of four hours is added to the end of the lease to prevent against clock drift between the DHCP client and server. On a Windows 2000-based DHCP server, leases are scavenged from the database if they meet the criteria of (ExpirationTime + 4 hours).

MORE INFORMATION

In Windows 2000, leases that are expired but fall within the grace period appear in Microsoft Management Console (MMC) as inactive leases. Statistically, they are counted with active and excluded leases as "In Use." However, any lease that falls within the grace period (inactive) may be issued by the DHCP server if the available leases fall to 0.

This behavior may become apparent if you are using short lease times and short scavenge intervals. The DHCP snap-in in MMC may display Scope Full icons (with an exclamation point on the Scope and Server icons) and the event log may contain event ID 1020. These notifications are based on the number of "In Use" addresses and occur even though inactive leases may be available to be distributed to requesting clients.

Sample event ID 1020:

Event Type: Warning
Event Source: DhcpServer
Event Category: None
Event ID: 1020
Date: 5/11/2000
Time: 5:32:24 PM
User: N/A
Computer: WIN2000
Description: Scope, 10.1.1.0, is 100 percent full with only 0 IP addresses remaining.

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

153072 (http://support.microsoft.com/kb/153072/EN-US/ ) Leases Retained in DHCP Database For One Day After Expiration